Solenoids are used in automobiles to control numerous devices such as clutch mechanisms or other transmission components. Additionally, it is possible for solenoids to be used in virtually any other hydraulically or pneumatically actuated vehicle system.
Referring now to FIG. 3 which shows a prior art valve 100, certain types of solenoids incorporate the use of a spool 102 that moves within a bore 104 of a valve portion of the valve 100. Typically, the valve 100 will have metering edges 103 on the spool 102 to allow fluid flow from a supply port 105 to a control port 107 and from the control port 107 to an exhaust port 109. When this type of valve 100 is actuated a downward force 108 is applied and the spool 102 moves downward in the bore 104. Fluid flows 110 from supply port 105 to control port 107, the fluid accelerates 112 between the supply port 105 and control port 107 creating a transient flow force which acts on the spool 102. This transient flow force acts to further open the spool 102 to the supply port 105 which in turn cause further acceleration of the fluid and increased downward transient flow forces 114 and so on. This has a very destabilizing effect on the valve 100 and is undesirable. Thus it is desirable to have a spool valve design in which any transient flow forces resulting from the valve opening to either supply or exhaust would act to close the valve and thus provide a stabilizing effect rather than a destabilizing one.